Scale changing system for stroboscopic indicators



2 Sheets-Sheet 1 Dec'. 9, 1947. A. M. sKELLETr SCALE CHANGING SYSTEM FORSTROBOSCOPIC INDICATORS Original Filed Oct. 9,1943

A. SKELLETT 2 Sheets-Sheet 2 V Orgna 1 Filed oct. 9, 1943 AM SKELLETT Afro/:MEV C v SCALE CHANGING SYSTEM FOR STROBOSCOPIC INDICATORS Dec. 9,194?.`

cision of the range measurement indicated by the range dial may beincreased by a predetermined factor when desired, a factor of ten beingpreferred. The range dial and the class A range indicator compriserotating elements each of which is stroboscopically illuminated only atthose instants when it presents a correct range reading.`

Fig. 1 shows the external appearance of the device as it may be arrangedfor the convenience of an operator. A portion of the indicator panel isshown at and is provided with windows |0| and |02 which may havesuitable frames or bezels. Behind the window |0| is mounted a range dialcomprising adrum |03, preferably translucent, upon which are placedindications such as a numerical scale of ranges. Provision is made forrotating the dial |03 and illuminating it -stroboscopically when acorrect range indication appears within the window |0| at a stationaryindex i011 that may be placed before the dial |03 to fix the exact pointof reading. Behind the window |02 is provided a rotating drum |05 with ahelical mark which is made to appear, when stroboscopically illuminated,as a vertical or nearly vertical line segment showing through thewindow. A

operator, observing the lines |01 to |09, inclusive, decides which oneof the objects represented by these lines is of special interest and heturns the knob to move the mark H0 to coincide with the desired line andadjusts the knob ||2 properly as explained hereinafter. The dials |03and l i3 are then stroboscopically illuminated to show the range of theselected object legibly and apparently stationary opposite the index|00. Another object may be thereafter selected by turning the knob li tobring the mark H0 in coin,- cidence with the second selected line and byreadjusting the knob l2 if need be, when the stro- 'boscopicillumination of the dials |03 and H3 will change to display the range ofthe second object. Within the window |0|, an illustrative range readingis shown on the expanded scale, indicating an object at a range of83,500 yards. This reading could be observed by bringing the markstationary scale |09 is provided for reading the v position of the linesegment when illuminated. The drum |05 may be illuminated a number oftimes during each revolution to produce a plurality of lines such as areshown at |01, |08 and |09 to indicate the ranges of objects atdifferent' distances. An arbitrarily movable line I0, which may bedistinguished from the lines |01 to |09, inclusive, in any suitable Vwayas for example by a different color of illumination, may be providedunder manual control of a knob to aid in selecting one of the distantobjects the range of which is to be indicated more precisely by thereading of the dial |03. Another knob ||2 may be provided to control anexpanded scale and the associated indication of a separate dial ||3mounted next to the dial |03 and appearing within the window |0i. Thedial |13 is stationary except when rotated manually by means of the knobl2 and is illuminated together with the dial |03 by the stroboscopiclight source. The mechanism associated with the panel |00 will bedescribed hereinafter with reference to Figs. 2, 3 and 4.

The manner in which the system is manipulated by the operator may bedescribed with reference to Fig. l, it being assumed that the nternalmechanism is operating and has been properly adjusted. First, it will beappreciated that the external appearance of any stroboscopicallyilluminated device will generally diifer from the external appearance ofthe same device'when viewed in ordinary illumination. For convenience inexplaining the operation of the system and at the same timeto make theView in Fig. 1 consistent with the other gures, it has been chosen tomake Fig. 1 a composite view. The

window |02 is assumed to be viewedwith the f H0 to coincide with theline |09. To dispense with the expanded scale and use what is commonlycalled the main scale, the knob ||2 may be turned until a numeral 0appears on the dial i|3 and a step further to operate a switchingmechanism which may be mechanically coupled to the knob l2 to switchover the electric circuit from a condition termed the expanded scalecondition to one termed the main scale condition as hereinafterdescribed.

Figs. 2 and 3 show the mechanism and circuits behind and associated withthe panel |00 of the device shown in Fig. 1.

In Fig. 2 a pulsing circuit 200 is shown connected both to an oscillator20|, preferably of ultra-high frequency, and a square wave generatortube 202 which with connected elements will be referred to as thestart-stop circuit. The oscillator 20| is connected to a suitableradiating system such as a dipole antenna 203 mounted at the focus of aparaboloidal projector 200. The output of the start-stop circuit isconnected to the grid circuit of a vacuum tube 205 in the anode circuitof which is connected a timing resistor 200 and condenser 201. Thecondenser 201 is also connected in the input circuit of a square wavegenerator tube 208, which serves as a narrow automatic range gate. Forthe reception of electromagnetie waves there may be provided adirectionally selective receiving system comprising a dipole antenna 209mounted at the focus of a paraboloidal reflector 2|0. The antenna 209 isconnected to the input of a radio receiver 2| the output of which iscomb-ined with the output of the tube 208 in the input circuit ofamplifying tube 2|2.

In Fig. 3 suitable power terminals 300 are shown connected to a motor30| to the shaft of which are keyed the dial |03, the drum |05 and apair of rotary switches or commutators 302 and 303. The commutator 302is connected with a source 300 of direct current and a timing resistor305k and either one of two condensers 305 and 301. Thedial |03 may betranslucent and may have mounted within it a ash lamp 308, which may bea neon lamp. The drum |05 may 'be opaque except for a helical slot 309which either may be open or may have a filling of a translucentmaterial. Within the drum |05 may be mounted flash lamps 3|0 and 3| l,preferably giving different colors of illumination such as a neon lamp3|0 and an argon lamp 3| The broad principle of operation and thesalient features ofA the structure of Figs. 1 to 3, inclusive, willfirst be briey given before presenting a more detailed description. Thepower supplied to the cies-sass the pulsing circuit 200 brieflyenergizes the .radio "transmitter '20| to deliver a short train `ofwaves to `the antenna 4203,fwhich trainisprojected as a pulsen-f`electromagnetic waves from the `projector :204. Simultaneously `withthe .energization .of the radio transmitter, the pulsing circuit.energzes the tube `202 to generate :a squareftopped pulse fusedtoiblockthe tube '205 .and start a charging current .in :the `resistor y200A.and condenser 207. :The tube 20.5 and associated timing velements-willbe-hereinafter referred toas the fast timing .cirxcilit. "The time4constant of the circuit is prefer- `V ably-so -predesigned that thepotential of the ,con-

"denser 207 willpass` 'through .a suitable range `of 'Values at asubstantially 'linear time rate duringA the brief time required for anelectromagnetic puise "to travel from the projector204 to the mostdistant .object the range of which is to be measlilrted and t0 .returnto the reflector 2 I0. The oomrnuta-tor 3.02 is arranged to connect thebattery .1354 to therother timing circuit .comprising the resistor 30.5and the condenser 30.6 to charge vthe `condoneer i305 at `a raterelatively slow compared `with Athe condenser 201 to cover a similarsuit- .ablerange of potentials on the condenser 306 dur- .ing ya singlerevolution .of the commutator. This .latter timing circuit willhereinafter be referred to as the slow timing circuit. .Due to therelatively slow rate of revolution of the mechanical system, it ispermissible to facilitate the description by assuming for the time beingthat the dial |03 vand drum |05 remain stationary during the timebetween til/cruises of the pulsing circuit 200. It is'also"permissibleat this 'point in :the description to assume that the potential of thecondenser 300 remains constant during the interval between two pulses, vProvision is .made to compare -theipotential pf the `conilerlser 306andthe potential of the condenser '210.1V in the l grid-cathode circuitof the tube 208. At some instant during `the period between "successivepulses .the potentials lof .the con- .dcnserstpe and 201 will be oftheproper reunion to c'h otherto unblo'ck thtube 208 and thereby Aini ate,a square-topped pulse therein. The circuit of the tube zus ispreferabiy so designedrnet t the square-topped pulse produced is one .of'relatively `short duration. The vtube 208, however, doesnot directly'connect withthe'flash lamps but `merelyenergizes or sensitizes theinput circuit `of 'the amplifyingtube 2 12. The tube 2 |'2 will oper-`ate 'tojiiash the 'larnpsj308 and 3i!) only ifa reiiectedpulse`is'received by the radio receiver A2| l dur-ing one fof the briefintervals when the tube -2|2 issensitized. The scale on `the dial|'03'is so *calibrated that whenthe lamp 308 flashes the correctIrangeof the ditsant object from which the relectedpulse was received isshown within the yfindow V40| Vopposite the stationary index |00. v"Thestationary'scale |00 adjacent the frame `|02 is so calibrated also `that'when the lamp 3|!) flashes the portion of the slot 300which i-silluminated andshows through the window |02 is opposite the samerange'freading on the scale |05 as iis simultaneously' appearing on thedial :103.

The illumination of the lamp 308 is preferably gate.

entirely independent of the reflected pulses and Aof :the `action of thetube 2|2 and Ymay be con- :trolled :solely by the setting of the rangegate to iiash once per revolution of the drum |05.

:Returning now to the .effect .of the rotation of Athemechanicalsystems, the shaft and attach- :ments will nolonger beconsidered as standing still. .During each interval between pulses the`dial lli-3,V drum |05 and the commutators 302 and 30:3 will have moveda small fraction of a revolution and the potential of the condenser 305will yfhave increased accordingly. `The dial |03 andthe drum |05 haveadvanced to a slightly higher range reading. The critical relation ofpotentials ofthe condensers 201 and 306 now occurs ata slightly laterepoch withrespect to thestart of the outgoing pulse from the projector204. As a result the tube 203 will energize the tube 2H? at ,acorrespondingly later epoch and the lamps `303 and 3 0 will flash .onlyin response to'an incoming reflected pulse from a somewhat more distantob- `.l`ect, the. range of which corresponds to the new reading ofthedial |03 and drum |05. `Accordingly, in each succeeding cycle of thepulsing circuit 200 the lamp control circuits'will be energized at theparticular epoch which corresponds to the range Vreading simultaneouslypresented `atjthe windows by the dial |03 and the drum |05. During eachrevolution of the .mechanical system the lamp control circuits will havebeen briefly energized successively at a succession of range readingsdistributed over the total'range of the apparatus. When the rangereading corresponds to the range of an object the reflected pulses from"that 'object willbe enabled to flash the lamps at least once during therevolution. As the speed of rotation is suicient to provide 30 flashesper second a substantially ickerless scale reading is obtained.

4In order that no pulses be lost due to being returned from objectshaving ranges that lie between the successive range readings for Vwhichthe lamp control circuits are energized, the automatic range gate shouldbe open each time for a suicient inter-Val to admit all returning pulsesfrom objects in a zone of a certain width.` l'lhe ratio of .thefrequencies of the fast and `slow timing .circuits :determines the widthof the zone `to be included by the range gate, or, as it may be :morebriefly termed, the width of the range rIhis should be as wide .as the.difference in the successive range readings for which the circuits are.energized to insure that allreflected pulses will operate .the flashlamp. For example, `with a motor speed of 30 revolutions per second anda pulsing rate of 2000 pulses per second, .the range gate should have awidth of about 1'1/2 per cent of the'maximum range, or 1500 yards in.100,000 yards. For an expanded scale of ten times the sensitivity ofthe main scale, the range gate Width in this example may be reduced .to:one-tenth or yards. The actual readings `may be more accurate .than thefrequency ratio indicates, due to the fact that unless thefre-...quencies fare .exactly 'commensurate succeeding mailings on the'.samerange will yaryslig'htly 7 and the eye will naturally read theaverage of the values presented by the scale.

The lamp 3|0 will flash once per revolution for each received pulse andwhen several pulses are received from objects at diierent ranges thelamp 3|0 will flash when the slot 309 is opposite each of a, number ofdifferent readings on the Vscale |06 producing a plurality of lines suchas |91 to |09, inclusive. The commmutator 303 will ash the argon lamp3|| once for every revolution of the drum |05 at a particular angularposition which kmay be controlled by means of the knob to produce anarbitrarily movable mark ||0 of a different color from the lines |01 to|09, inclusive. By moving the mark H0 to coincide with one of the linessuch as |91 to |09, inclusive, the lamp 308 will be made to flash toshow a precise reading of the range corresponding to the particular lineselected by the operator.

The purpose of the expanded scale is to cover a restricted group ofranges with a more precise balance of voltages in the input of the tube208 as well as with a narrower range gate. The particular portion of thescale |06 to be covered by the expanded scale is indicated by the dial||3 which places an additional digit in front of the reading of thescale |03 by means of a mechanism which will be more fully describedhereinafter.

The circuits shown in Fig. 2 will now be described in somewhat greaterdetail.

Start-stop circuit The start-stop tube 202 may contain, in a singleenvelope, if desired, two triodes 2|3 and 2|4, the triode 2|3 includinga cathode 2|5, a grid 2|6, and an node 2|1 and the triode 2M including acathode 2|8, a grid 2|9 and an anode 220. A supply source 22|, such as abattery, may have its negative terminal grounded as at 222. The positiveterminal of the source 22| may be connected to the anode 2|? through ananode load resistor 223 as well as directly to the anode 220 and througha grid load resistor 225 to the grid 2|9. The cathodes 2|5 and 2|8 maybeconnected to ground through cathode resistors 225 and 226. The pulsingcircuit 200 may be connected to the grid 2li:` by a blocking condenser221. A grid resistor 228 is preferably connected between the grid 2| 6and the common terminal of the cathode resistors 225 and 225. A couplingcondenser 229 is provided between the anode 2|? and the grid 2 I9.

In the operation of the start-stop circuit, the triode ZIA is normallyconducting because of the connection of the grid 2|9 with the positiveterminal of the supply source 22| through the resistor 221i. Theanode-cathode current of the triode 2| flowing through the properlyproportional resistor 225 provides a blocking potential upon the grid2|8 which renders the triode-2l3 normally non-conducting. The connectionof the grid 2|9 to the positive terminal of the source 22| through theresistor 224 renders the grid potential positive with the result thatgrid current ows through the triode 2id and adds to the biasing currentin the resistor 225. The triode 2|3 has substantially the full supplyvoltage impressed across between its anode and cathode although, asaforementioned, anode current is blocked by the negative potentialimpressed upon the grid 2|6 by the current flowing in the resistor 225.This condition of the start-stop circuit is a 8 stable one but it may bedisturbed by the receipt of a pulse from the circuit 20|).

The pulsing circuit-l 200 is preferably arranged to impress a pulse uponthe grid resistor 228 through the blocking condenser 221, the pulsebeing of such polarity as to render the grid 2|6 more positive withrespect to the cathode 2|5.

YThe pulse. is preferably of sufficient strength to overcome thenegative bias impressed upon the grid 2|6 by the resistor 225, therebyrendering the triode 2|3' conductive. The flow of current from thesource 22| through the resistor 223 and the anode-cathode circuit of thetriode 2|3 produces a drop in the potential of the anode 2|1. As aresult, the charged condenser 229 begins to discharge through theresistor 224 and at the same time the condenser 229 effectively places anegative bias upon the grid 2|9, thereby causing the triode 2|4 to cutoff its own anode-cathode current. The cessation of the current in thetriode 2 ld removes some of the negative bias from the grid 2|6 andenables the supply source 22| to maintain the anode-cathode current inthe triode 2 I3 even though meanwhile the activating pulse from thecircuit 200 may have ceased. The condenser 229 continues to dischargethrough the resistor 224 and when suiiiciently discharged, the triode 2Magain becomes conductive and its anode-cathode current restores thenegative bias in the resistor 225 to cut oi the anode-cathode current inthe triode 2|3, thereby returning the start-stop circuit to the originalstable condition. The time required for the cycle of operations in thestart-stop circuit is determined mainly by the capacitance of thecondenser 229 and the resistance of the resistor 224. The cycle may berepeated by supplying successive pulses to the grid 2|6 from the pulsingVcircuit 200. The start-stopV circuit develops a good square-topped wavebetween the cathodes 2|5 and 2|8 and the ground 222 which wave may beimpressed upon the grid of the trigger tube 205 by means of a blockingcondenser 230 and a grid resistor 280.

Fast timing circuit The fast timing circuit comprises the vacuum tube205, the resistor 206 and the condenser 201. The tube may be a pentodehaving a cathode 23|, a control grid 232, a screen grid 233, asuppressor grid 234 connected to the cathode, and an anode 235. Thecathode 23| may be grounded and the anode 235 may be connected to thepositive terminal of the source 22| through the resistor 206. Y

In the operation'of the fast timing circuit, the grid 232 normallymaintains the tube 205 in a conducting condition due to the potentialdrop across the resistors 225 and 226 being balanced with respect; tothe grid 232 by a charge on the condenser 230. When the potential acrossthe resistors 225 and 226r falls during the operation of the start-stopcircuit, this drop in potential transmitted through the condenser 230impresses a negative potential upon the grid 232, thereby blocking thetube 295 and permitting charging current to flow to the condenser 201through the resistor 206. At the end of the square-topped pulse when thepotential diierence across the resistors 225 and 226 is restored, thegrid 232 returns to substantially ground potential, rendering the tube205 conducting and permitting rapid lisscharge of the condenser 201through the tube Automatic range gate The automatic range gate comprisesthe square Wave generator 288 and associated circuits; Ther tube 288 maycontain, in a single envelope, il.` desired, two triodes 236 and 231,the triode 236 including a cathode 238, a control grid 239 and an anode248 and the triode 231 including a, cathode 24|, a control grid 242 andan anode 243. The cathode 24| may be directly grounded and the cathode238 may be connected to ground through a coupling condenser 244. Theanodes 248 and 243 may be connected to the positive terminal of thesource 22| through anode circuit resistors 245 and 246, respectivelylThe anodeS- 248 and 243` may be cross-connected to the grids 242 and239, respectively by coupling condensers 241 and 248. The grid 239 maybe connected to the positive terminal of the condenser 281 through acoupling resistor 243. The grid 242 may be connected to ground througheither one of two resistors 258 and 25| under the control of a switch252.

In the operation of the automatic range gate.

the potential of the condenser 281 is continuously compared with thepotential of a selected one of the condensers 386 and 381 in thegrid-cathode circuit of the triode236. The potential of the condenser281 acts` by virtue of direct connection` in the grid-cathode circuit,while the potential of condenser 386 or 381 is impressed upon thecathode 238. The potential of the cathode 238 is thus changing at a slowrate` and the potential of the grid 239 is changing at the fast rate. Atthe start of each fast cycle the grid potential is more negative withrespect to that of the cathode 238 than the cut-off voltage of thetriode and as it rises this cut-off potential is reached and the triode236 `starts to conduct. Before this critical potential relation isreached the triode 231 is conducting due to the grid 242- beingconnected to the cathode 24| through one of the resistors 258 and 25|,andthe coupling condenser 241 contains a charge of substantially thefull voltage of the source 22|. When the triode 236 becomes conducting,its anode potential falls due to the now of current in the resistor 245,and this potential drop is impressed on grid 242 through condenser 241,thereby immediately blocking the triode 231. The condenser 241 rapidlydischarges through the` resistor 258 or 25|, removing after a deliniteinterval the blocking potential from the grid 242- and permittingcurrent to now again. It will be noted that while the triode 231 Wasblocked, the coupling condenser 243 was being charged through theresistor 246, 248 and the condenser 281. When the triode 231has resumedconductivity, the charge on the condenser 248 is eiectively thrownacross Y between the grid 239 and the cathode 23.8 to form a blockingpotential to aid in restoring the triode 236 to thenorma'l condition.The generator 2,88 i

thus produces a'square-topped pulse preferably of brief duration whichis impressed upon. the input circuit of the dashing tube 2|2. During thenormal blocked condition of the triode 236, the. triode 231 isconductive and hence the anode l may be varied by means of the switch252 toa 150. select one or the otherof theresistors 258 and 25| 'through`which to discharge the condenser 241.

Flashing circuit The ashing circuit comprises the tube 2 I2 andassociated elements. The square-topped Wave from the generator 288 isimpressed upon the flashing circuit through a coupling condenser 253iThe flashing tube 2|2 may contain, in a .single envelope, if desired,two triodes 254 and 255, the triode 254 including a cathode 256, a grid251 and an anode 258and the triode 255 including a cathode 259, a grid268 and an anode 26E. The ungrounded side of the radio receiver 2|| maybe connected to the grid 251 through a coupling condenser 262 and theoutput of the automatic range gate may be connected into thegridecathode circuit 0f the triode 254. by` means of the couplingcondenser 253. The tube 212- comprises two stages of amplication.Normally the grid 251 is biased more negative than its cut-off potentialso that echoes from the radioY receiver cannot get through to operatethe flashf ing lamps 388 and3|8. When the range gate is impressed onthis grid it brings its potential tocut-off and the echoes, Which are ofpositive po.- tential can then get through to triode 2.55 where they areamplied for use in triggering off the flash tubes 388 and 3| 8. Thus thetube 2|2 is operated when a signal is received by the radio` receiver 2|provided at the same time the tri,- ode 254 isA unblocked by the` actionof the tube 28.8.

Flash lamps The flash lamps 388, 3|8 and 3|| are prefer ably of thethree-electrode cold type. The tubes 388, 3|8 and 3H have anodes 312,3|3 and 3|4, respectively, all of which are permanently connected acrossa condenser 2,66, and a series inductance 268 through a lead 3|5 andthrough the lead 3|5 Iarid a resistor 261 to a junction point 264 in apotentiometer acrossv the` source 22|. The tube 388 has a pair ofcontrol electrodes 3|6 and. 3 |1V and the tubes 3|8 and 3|| havecorresponding pairs of control electrodes 3|8, 3 |9 and 328, 32|. Groundconnection is supplied over a lead 322 in a permanent connection to thecontrol electrode 3|8 of the tube 3|8 so that this tube Willflashwhenever an exciting potential is impressed upon` its second controlelectrode 3| 6. Ground connection is supplied to the control electrodes3|6'and 328 of the tubes 388 and 3| respectively, through a lead 323, abrush 324, a conductive band 325 of the commutator 333, a brush 326 tovground at 321 only during the passage of the brush 324 over theprojection 328 of the band 325. At all other timesthe brush 324 connectsthe electrodes 3|6 and 328 through another brush 343 to a disablingpositive potential such as is supplie-d by a battery 358. The secondcontrol electrodes 311 and SiS of the tubes 388 and 3|8, respectively,are connected through a lead 329 to a junction point 265 in the outputcircuit of the iiashing tube 2 |2. These tubes 388 and 3|8 receiveoverthe lead 3231 a flashing voltage upon receipt of a reflected radio waveby the system at a time when the automatic range gate is open. Thecontrol elece trode 32| of the tube 3H is permanently connected to thepositive terminal of a source 338 'illustrated as a battery. The battery338 becomes effective to aish the tube 3| whenever the ground connectionis applied to the other control electrode .328 bythe commutator 383.

VIn the operation of the tubes 388, 3 I8 and 3| it l1 will be evidentfrom the foregoing description of the connections that the tube 3| willbe operated once during each revolution vof the commutator 303 when thebrush 324 crosses the projecting segment 328. The tube 308 will ashprovided a radio impulse is received while the automatic range gate andthe manual range gate are-both set for substantially the correct range.The tube 3 I0 will operate independently of the manual range gatewhenever a radio impulse is received during the open condition of theautomatic range gate. Each flash lof the lamps discharges the condenser266 which is then recharged at a dennitek rate through the resistor 261and the inductor 268 in time for the next flash.

Slow timing circuit The slow timing circuit comprises the source 300,themotor 30|, the commutator 302, the potential source-304, the timingresistor 305 and the timing condensers 306 and 301. The source 304 isconnected across a pair of serially connected potentiometers 33| and332. Assuming the potentiometers 332 and 33| to be set each on step 8 asillustrated, a circuit is formed through a flexible lead 333 to theresistors 305, through a brush 334 on the commutator 302 to anotherbrush 335 and then through a lead 336, to one of the condensers 306 and301 and then through a lead 331 and a exible lead 338 to step 8 of thepotentiometer 33| and thence to ground. The commutator 302 comprises twoconductive bands 339 and 340. The brush 334 runs continually on the band340 and a brush 34| on the band 339. The brush 335 runs upon the band340 except during a certain portion of each revolution when the brush335 rests upon a projection 342 which is an integral part of the band339. While the brush 335 rests upon the projection 342, the condenser306 or 301 is short-circuited. When, during the revolution of thecommutator 302, the projection 342 moves away from the brush 335, thecondenser 306 or 301 begins to charge through the resistor 305.

The charging of the condenser continues at a substantially uniform rateuntil the projection 342 is again brought under the .brush 335 when thecondenser is quickly discharged and made ready for a repetition of thecharging cycle. The potentiometers 33| and 332 are preferably soarranged that the eifective charging voltage is the same regardless ofthe steps occupied by the varie able contacts of the potentiometers.

Rotating mechanical system The commutators 302 and 303 are preferablykeyed to the shaft of the motor 30|. The dial |03 and the drum |05 arepreferably xedly attached to the shaft by suitable means such as spiderstructures 342 and 343, respectively. The dial I3 is preferably mountedfreely on the shaf and may be geared to the knob |2 in known manner as,for example, by means of a suitable com bination of racks and pinions.The brush 324 is preferably mounted on a spider structure 344 whichrides freely on the shaftand is geared to the knob through anothersuitable combina tion of racks and pinions. The remaining brushes arestationary and may be supported in any suitable manner. The lamp 308 maybe mounted inside the dial |03 and the lamps 3 I0 and 3| inside the drum|05. The necessary'leads to the lamps may be introduced through thespace between the dial |03 and the drum |05.

12 Angular displacement of the rotating parts In setting the commutators302 and 303 and the dial |03 and drum |05 on the shaft, the followingconsiderations should be observed as to the relative angular positionsof these elements. The dial 03, in a system intended to measure rangesup to 100,000 yards will preferably have a scale reading from 0 to100,000 yoccupying a major portion of the periphery of the dial. A blanksegment, shown in Fig. 3 for clarity as one-sixth of the complete circleis reserved to cover the inter-- val of time required for the dischargeof the slow timing circuit but this interval may be shortenedconsiderably in practice. The helical mark 309 occupies the sameproportional part of a complete circumference of the drum |05 as thenumerical scale occupies in the complete circumference of the dial |03.The dial |03 and drum |05 are to be set in such a relative angularposition that the reading of the dial 03 against the index |04 at thewindow |0| is identical With the reading of the mark 309 against thescale |05 at the window |02. The angular relation between the commutator302 and the brush 335, should then .be such that when the trailing edgeof the segment 342 of the commutator leaves the brush 335, the dial |03registers zero against the index |04. The angular position of thecommutator 303 on the shaft may be determined arbitrarily.

M azn scale When the expanded scale is not in use, the apparatus is saidto be operating on the main scale. The potentiometers 33| and 332 areeach provided with ten taps or positions, numbered from 0 to 9,inclusive, which are used with the expanded scale. An additionalposition M is provided adjacent to the zero position for use whenoperating with the main scale and is di rectly connected electrically inthe potentiometer with the adjacent position 0. Potentiometer arms 345and 346 for the respective pctentiometers 33| and 332 are provided andmay be in sulatingly attached to a bar 341 in the rack and pinion'systemoperated by the knob ||2. In using the main scale the knob ||2 isrotated to bring the arms 345 and 346 on to the respective M positionsof the potentiometers. This operation results in a rotation of the dialI3 through zero to one position beyond zero, at which position there isno number showing at the window |0|. The switches 252 and a switch 348controlling the selection of the condensers 306 and 301 are preferablymechanically coupled to one of the potentiometer arms 345 or 346 in sucha manner that the switches 252 and 348 are both operated Whenever thearm 345 passes from the zero position to the M position or vice versa.For the main scale, the switches 252 and 348 are operated into the Mposition bringing the resistor 25| and condenser 301 into circuit forthe main scale and the resistor 250 and condenser 306 for the expandedscale. In operation with the main scale, one terminal of the condenser301 is grounded so that the potential impressed upon the condenser 244by the slow timing circuit is simply the potential of the condenser301'. The resistor 25| is proportioned to give the desired width to theautomatic range gate. The reading in the window I0| is shown by thenumber appearlng on the dial |03.

Expanded scale .In operation with the expanded scale, when one of themarks such as |01, |08 and |09 appearing at the window |02 has beenselected by the operator, the knob H2 is turned to bring the first digitof the range of the selected line into View in the window lili. Forexample, if the line 00 is chosen (reading approximately 83,000 yards onthe scale |06) the digit 8 is brought into View in the window 10i, asshown in Fig. 1. This operation moves the potentiometer arms 345 and 346to the position 8 on the potentiometers 30| and 332, as illustrated inFig, 3. It also operates the switches 252 and 348 to the -9 -po sition,bringing into circuit the resistor 250 and the condenser 306. Thecondenser 305 is now in series with a potential provided between groundand position 8 of the potentiometer 33| and this potential is added onto the potential of the condenser 300 in the condenser 2134 forcomparison with the potential in the fast timing circuit. The potentialimpressed upon the slow timing circuit is the same regardless of theposition of the potentiometers, when, asis preferable, the potentialbetween each pair of corresponding positions on the two potentiometersis the same. The resistor 250 is preferably designed to reduce the widthof the automatic range gate to onetenth the value used with the mainscale. The condenser 300 is preferably made 'ten times the capacity ofthe condenser 301 so that during the period of a single revolution thecondenser 305 will acquire a potential only one-tenth as great as thatattained by the condenser 301 when using the main scale. The potentialdiierence between two adjacent positions of the potentiometers is thusspread out by means of the condenser 306 to occupy a complete cycle ofthe slow timing circuit, The reading in the window 10| is comprised bythe reading of the dial 103 prexed by the digit exhibited by the dialH3.

In the system as illustrated, switching over to the expanded scaleexpands the range covered by the drum i 05 and the images in the longwindow |02. The scale |06 will then represent hundreds of yards insteadof thousands as for the main scale and as the knob H2 is turned theportion of the total range covered by the scale |05 will be moved alongthe total range along with the indication of the dial H3.

What is claimed is:

1. A scale changing system comprising, for a main scale, a timingcircuit having a predetermined time constant, a source of electromotiveforce of substantially constant potential, means to connect said sourceof electromotive force to said timing circuit to generate a potential insaid timing circuit Varying at a predetermined time rate, and means toshift to an expanded scale, said means comprising means to change thetime constant of the timing circuit to a predetermined greater timevalue, and means to add a predetermined substantially constantelectromotive force to the varying potential generated in said timingcircuit.

2. A decimal scale expansion system comprising, for a main scale, atiming circuit having a predetermined time constant, a source ofelectromotive force of substantially constant potential, means toconnect said source of electromotive force to said timing circuit togenerate a potential in said timing circuit Varying at a predeterminedtime rate, a decimal scale indicating a series of values correlated withthe instantaneous value of the potential of said timing circuit, andmeans to expand the said scale between any two decimal subdivisions,said means comprising means to multiply the time constant thecombination of said indicated digit and said decimal scale reading.

3. A scale changing system comprising a timing A circuit having apredetermined time constant, a source of electromotive force ofsubstantially constant potential connected to said timing circuit togenerate a potential in a portion of said timing circuit varying at apredetermined time rate, means to change the time constant of the timingcircuit to a new value, and means to make a change in the potential ofsaid source of electromotive force.

4. A decimal scale expansion system comprising a timing circuit having apredetermined time constant, a source of electromotive force ofsubstantially constant potential connected to said timing circuit togenerate therein a potential varying at a predetermined time rate, adecimal scale indicating a series of values of the instantaneouspotential of said timing circuit, means t-o multiply the time constantof the timing circuit by a factor of ten, means to add a predeterminedsubstantially constant electromotive force to the varying potentialgenerated in said timing circuit, and means to display a prex digitadjacent to said decimal scale, said prefix digit being correlated withthe amount of said added electromotive force.

5. A scale changing system comprising a fast timing circuit and a slowtiming circuit, means connected to said fast timing circuit generatingtherein a potential varying at a predetermined fast time rate, a sourceof electromotive force of substantially constant potential connected tosaid slow timing circuit to generate therein a potential varying at apredetermined slow time rate, a source of potential variable in stepsconnected in series with respect to the said varying potential in saidslow timing circuit, means comparing the sum of said serially combinedpotentials with the said Varying potential in said fast timing circuit,means displaying an indication of the instantaneous value of saidVarying potential in said slow timing circuit, and means displaying anindication of the Value of said potential that is variable in steps.

6. A scale changing system comprising a fast timing circuit producing apotential varying at a predetermined fast time rate, a slow timingcircuit producing a potential varying at a predetermined slow time rate,a source of electromotive force adjustable as to potential in aplurality of steps, means connected with both of said timing circuitsand with said source of adjustable electromotive force and producing anindication upon a condition of instantaneous equality between said fastvarying potential on the one hand and the sum of the potentials of saidslow timing circuit and said source of adjustable potential on theother, and means coupled to said source of adjustable potential anddisplaying an indication of the value of said adjustable potential undersaid condition of equality.

ALBERT M. SKELLETT.

